Methane Gas Wellhead

ABSTRACT

A methane gas wellhead, having: a body having a pair of side outlets and a top outlet; a mandrel dimensioned to be received into the top outlet; and a cover plate dimensioned to be received over the mandrel, and to hold the mandrel in the top outlet when the cover plate is secured to the top of the body; or a body having a pair of side outlets and a top outlet; and a mandrel dimensioned to be received into the top outlet, wherein the mandrel is a negative pressure mandrel, and wherein the top outlet and the mandrel are dimensioned to receive an O-ring seal therebetween.

RELATED APPLICATION

The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/050,030, entitled “Methane Gas Wellhead”, filed May 2, 2008, which is expressly incorporated herein in its entirety for all purposes.

TECHNICAL FIELD

The present invention is related to methane gas wellheads.

BACKGROUND OF THE INVENTION

Extraction of methane gas from coal beds may be done in a variety of ways. First, a methane gas well is drilled into a coal bed. Next, water in the coal bed may be removed such that the methane in the coal bed can be released. After the water level in the coal bed has been reduced, methane gas is then able to flow up out of the drilled wellhead. The water in the coal bed may be removed by pumping the water out, or by injecting gas into the coal bed, or both. At different times, gases are injected into and/or removed through the wellhead. For example, the initial flow out of the wellhead is returning injected gas, followed by methane, and possibly even followed by water. Moreover, at various times, water may instead be injected into a well to “flush” the well. However, at most times, water is simply removed up through the wellhead. As can therefore be appreciated, a coal bed methane wellhead must be designed for the injection and removal of both gas and water therethrough.

Moreover, at different times, a methane gas wellhead may be operated at either positive or negative pressures. For example, the initial pressure of the wellhead is typically positive (e.g.: when gasses are injected to reduce the water level) and thereafter when the methane gas is first extracted. After a period of time, the pressure in the well drops, decreasing gas extraction yields. There are several solutions to extract more methane at this stage. First, the well may be re-pressurized (by injecting gas or water through the well head); or, alternatively, the gas pressure (and water level) in the well may instead be decreased such that the well is essentially “vacuumed out”. Different conditions and considerations apply if the methane is disposed within a dry coal bed, or within an aquifer.

Unfortunately, it is not easy to switch between positive and negative pressure mandrels in a traditional methane gas wellhead. Rather, traditional methane gas wellheads tend to be suited to handle either a positive pressure mandrel or a negative pressure mandrel. Thus, considerable reworking and/or equipment setup is required when changing from a positive pressure mandrel to a negative pressure mandrel (or vice versa). Another important consideration when changing mandrels is safety. Specifically, it is important to remove positive pressure mandrels in a safe way (since they are under pressure and would simply “blow out” of the top of the wellhead in the absence of a safety system). It is also desirable to have a proper safety system in place when a positive pressure mandrel is removed such that a “blow out protector” or “diverter” can by fastened to the top of the wellhead.

As can therefore be appreciated, the need exists to provide a safe and easy to use easily convertible mandrel system having parts that can quickly and easily be interchanged/re-connected when switching between positive and negative pressure mandrels. It is also most desirable that this system have multiple safety features for holding positive pressure mandrels within the wellhead.

SUMMARY OF THE INVENTION

The present invention is a novel gas well head. It is especially well suited for use in oxygen free low-pressure coal bed methane extraction. A unique advantage of the present invention is its versatility as it can be used with both positive-pressure or negative-pressure mandrels. As such, the present invention is “frac friendly” permitting blow out to charge the well. In addition, the present invention has multiple safety features that can hold a positive pressure mandrel securely within the wellhead. This is especially useful when the wellhead is being connected to a drilling rig.

In one embodiment, the present invention is a methane gas wellhead, comprising: a body having a pair of side outlets and a top outlet; a mandrel dimensioned to be received into the top outlet; and a cover plate dimensioned to be received over the mandrel to hold the mandrel in the top outlet when the cover plate is secured to the top of the body.

In another preferred embodiment, the present invention provides a methane gas wellhead, comprising: a body having a pair of side outlets and a top outlet; and a mandrel dimensioned to be received into the top outlet, wherein the mandrel is a negative pressure mandrel, and wherein both the top outlet and the mandrel are dimensioned to receive an O-ring seal therebetween.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 to 7 show various views of the present wellhead with a positive pressure mandrel.

FIG. 8 is a top perspective view of a negative-pressure mandrel for use with the present invention.

FIG. 9 is a bottom perspective view of the negative-pressure mandrel of FIG. 8.

FIG. 10 is a schematic illustration of the present system in operation with a negative pressure mandrel.

DETAILED DESCRIPTION OF THE FIGURES

The attached FIGS illustrate the present well head in accordance with the present invention. An element by element parts listing is as follows (like parts have like numbers in the figures):

Well head—10

Body—20

Top Outlet—21

Side Outlet—22

Ring Groove—23

Bottom—24

Radial Aperture—25

Radial Fastener—26

Mandrel—30 (positive-pressure mandrel—30A; negative-pressure mandrel—30B)

Opening—32

O-ring—31

Opening—34

Notch—35

Protrusion—36

Cover Plate—40

Casing—50

Tubing—52

Submersible pump—54

Well—W

As seen in FIGS. 1 to 7, the present invention provides a methane gas wellhead system 10, comprising: a body 20 having a pair of side outlets 22 and a top outlet 21. A positive pressure mandrel 30A is dimensioned to be received into top outlet 21. A cover plate 40 is dimensioned to be received over mandrel 30A to hold mandrel 30A in top outlet 21 when cover plate 40 is secured to the top of body 20. This prevents positive pressure mandrel 30A from simply being “blown out” of the top of wellhead system 10 (due to the pressures within the well). In addition, cover plate 40 also serves as a “weather guard” for the top of the wellhead. Cover plate 40 may comprise a two piece cover plate, as illustrated. Such a two-piece design has the advantage of ease of handling by an operator.

Preferably, body 20 has a bottom threaded outer end 24. As such, it can be securely fastened onto the top of a coupling on a casing that is cemented at the top of the drilled well. (See FIG. 10). Preferably, each of the pair of side outlets 22 are also threaded on their interior surfaces, and are flanged as well. The advantage of threading side outlets 22 is that it substantially increases the working pressure capability of the system when the system is connected onto gas injection and gas extraction lines. Moreover, being both threaded and flanged, it is possible to connect different piles/lines using either method.

As illustrated, mandrel 30A in FIGS. 1 to 7 is a positive-pressure mandrel. Positive pressure mandrel 30A comprises at least one O-ring 31 disposed therearound; with a pair of top-to-bottom openings 32 and 34 passing therethrough. Opening 32 may be dimensioned to connect to a water line which may alternately be used for pumping water out of the well (with a submersible pump positioned at the bottom end of the water line deep in the well), or for injecting water into the well. (See tubing 52 FIG. 10). Opening 34 may be dimensioned to pass various electrical connections therethrough, such as electrical connections for the submersible pump (See pump 54 in FIG. 10).

In optional embodiments, the at least one O-ring 31 comprises a pair of O-rings, as illustrated. It is to be understood, however, that alternate designs of positive pressure mandrel 30A are all encompassed within the scope of the present invention. As such, positive pressure mandrel 30A may have no holes (like 32 and 34) passing therethrough, or any number of holes passing therethrough.

Preferably, body 20 further comprises a plurality of radial apertures 25, with radial fasteners 26 being dimensioned to be received therein. In this embodiment, radial fasteners 26 and mandrel 30A are dimensioned such that radial fasteners 26 are received into a notch 32 on the side of mandrel 30A (i.e.: the notch formed slightly above a top edge of protrusion 36 on which O-rings 31 are located). In this position, the inward ends of radial fasteners 26 are positioned above the widest portion (i.e.: above a tope edge of protrusion 36) of positive pressure mandrel 30A. Notch 32 thereby assists in holding positive-pressure mandrel 30A down in top outlet 21. This feature is especially useful in that fasteners 26 will hold mandrel 30A down in position when cover plate 40 is removed.

In addition, cover plate 40 is also preferably dimensioned such that its inner circumference rests on notch 32, thereby also holding positive-pressure mandrel 30A into top outlet 21. A plurality of bolts pass through holes in the top flanged end 21 of body 20 and through holes in cover plate 40, thereby bolting cover plate 40 onto top 21 of body 20. Together, fasteners 26 and cover plate 40 both act separately to hold mandrel 30A down in position. Specifically, whenever cover plate 40 is removed (for example, when securing a rig or blow out protector onto the top of system 10 to remove mandrel 30A up therethrough), fasteners 26 will hold mandrel 30A down in position. As such, the present invention has two different safety systems to prevent a blowout of the mandrel.

FIGS. 8 and 9 illustrate a negative-pressure mandrel 30B. This negative pressure mandrel 30B is typically used after a period of time when the well productivity has dropped, and when gas does not flow out of the well as freely. In this situation, it is desirable to pull a vacuum on the well to maximize gas production. As can be seen in FIG. 9, mandrel 30B comprises a ring groove 33 dimensioned to receive an O-ring therein. This O-ring is also received into ring groove 23 in top outlet 21 (see FIG. 1). Thus, the O-ring is positioned between top 21 of body 20 and the bottom of negative-pressure mandrel 30B. The advantage of placing an O-ring into ring grooves 33 and 23 is that seals the system under vacuum pressure, while also preventing dirt and debris from entering the wellhead. Specifically, the O-ring in ring grooves 33 and 23 prevents oxygen from entering the well when a vacuum is pulled, resulting in a substantially “oxygen free wellhead”. Negative pressure mandrel 30B is preferably flanged (as shown) and bolts onto the top of top outlet 21 (instead of sitting down in the wellhead like positive pressure mandrel 30A). When negative pressure mandrel 30B is used, the openings for fasteners 26 can be plugged, preventing oxygen from passing down into the well. Thus, a substantially oxygen free environment will be created in the well.

Lastly, FIG. 10 is an illustration of the system in operation using positive pressure mandrel 30A, as follows. System 10 is installed as follows. First, a well W is drilled. A casing 50 is cemented around the open top end of well W. Next, bottom end 24 of system 10 is fastened onto casing 50. (This may optionally be done with a threaded connection on bottom end 24). Mandrel 30A then supports a long pipe 52 having a submersible pump 54 at its bottom end. Submersible pump 54 is used for pumping water out of well W through pipe 52 (and out through hole 32 in mandrel 30A). In various embodiments, pipe/tubing 52 may be of any length but is commonly from 200 ft to 3,000 ft long. Tubing 52 is suspended from mandrel 30A, and mandrel 30A preferably rests in a notch on the interior of top outlet 21. During assembly, tubing 52 is first suspended the desired depth into well W, by a rig (not shown). Next, mandrel 30A is placed into position sealing the well (and supporting the tubing 52) as shown. A rig (not shown) then screws onto the top of the mandrel and sets tubing 52 at a correct position with respect to the mandrel. If no electrical pump is used, then opening 34 in mandrel 30A can instead be sealed with a bull plug. Next, a gas source (not shown) may be connects to a first side outlet 22A for injecting gas into well W. A gas outlet pipe may then be connected to opposite side outlet 22B for extracting gas from well W.

In embodiments of the present invention built by the inventor, pressures in system 10 of 740 psi have been achieved. However, by instead using the threaded interiors of side outlets 22 for making connections to flanged ball valves, pressures up to 1,500 psi can be achieved. It is to be understood, however, that the present invention encompasses various pressure ranges and is not limited to any one operating pressure range. In various embodiments, tubing 52 can be 2⅜″, 2⅞″ or 3½″ (or other dimensions). It is also to be understood, however, that the present invention is not limited to any specific working pressures or dimensions. 

1. A methane gas wellhead, comprising: a body having a pair of side outlets and a top outlet; a mandrel dimensioned to be received into the top outlet; and a cover plate dimensioned to be received over the mandrel, and to hold the mandrel in the top outlet when the cover plate is secured to the top of the body.
 2. The methane gas wellhead of claim 1, wherein the mandrel is a positive-pressure mandrel.
 3. The methane gas wellhead of claim 1, wherein the mandrel is a negative-pressure mandrel.
 4. The methane gas wellhead of claim 1, wherein the body has a bottom threaded end.
 5. The methane gas wellhead of claim 1, wherein the interior of the side outlets is threaded.
 6. The methane gas wellhead of claim 2, wherein the positive pressure mandrel comprises: at least one O-ring disposed around the mandrel.
 7. The methane gas wellhead of claim 6, wherein the at least one O-ring is a pair of O-rings.
 8. The methane gas wellhead of claim 2, wherein the positive pressure mandrel comprises: a pair of openings passing therethrough, the pair of openings comprising a first opening dimensioned to connect to a water line, and a second opening dimensioned to connect to electrical connections.
 9. The methane gas wellhead of claim 1, wherein the cover plate is a two piece cover plate.
 10. The methane gas wellhead of claim 1, wherein the body comprises a ring groove dimensioned to receive an O-ring therein, when an O-ring is positioned between the top of the body and the cover plate.
 11. The methane gas wellhead of claim 1, wherein the body comprises a plurality of radial apertures, and further comprising a plurality of radial fasteners dimensioned to be received into the radial apertures.
 12. The methane gas wellhead of claim 11, wherein the radial fasteners and the mandrel are dimensioned such that the radial fasteners are received into a notch on the side of the mandrel.
 13. The methane gas wellhead of claim 1, further comprising: a plurality of bolts passing through holes in the top of the body and the cover plate, thereby bolting the cover plate onto the top of the body.
 14. The methane gas wellhead of claim 1, wherein each of the pair of side outlets are threaded.
 15. The methane gas wellhead of claim 1, wherein each of the pair of side outlets are flanged.
 16. The methane gas wellhead of claim 1, wherein the top outlet is flanged.
 17. The methane gas wellhead of claim 1, wherein the wellhead is designed for use with a low pressure, oxygen free coal bed methane source.
 18. A methane gas wellhead, comprising: a body having a pair of side outlets and a top outlet; and a mandrel dimensioned to be received into the top outlet, wherein the mandrel is a negative pressure mandrel, and wherein the top outlet and the mandrel are dimensioned to receive an O-ring seal therebetween.
 19. The methane gas wellhead of claim 18, wherein at least one of the bottom end or side outlets is threaded.
 20. The methane gas wellhead of claim 18, wherein the negative pressure mandrel comprises: a pair of openings passing therethrough, the pair of openings comprising a first opening dimensioned to connect to a water line, and a second opening dimensioned to connect to electrical connections.
 21. The methane gas wellhead of claim 18, further comprising: a plurality of bolts passing through holes in the top of the body and the negative pressure mandrel, thereby bolting the negative mandrel onto the top of the body.
 22. The methane gas wellhead of claim 18, wherein each of the pair of side outlets are threaded or flanged. 